Genre: ARPG, Free to Play (100% free to play, no pay to win, "ethical" microtransactions only)

To start with here is the Open Beta Trailer for Path of Exile:

Path of Exile is a nifty little indie ARPG game, completely free to play with the option of donating via ethical microtransactions (aesthetic mtx's only). The big official launch is coming Oct 23rd (it is in open beta atm, no requirement to get in + no wipes on launch) and it looks absolutely phenomenal even compared to the already stellar open beta version. The real reason to love this game is its absolute and massive depth, you can spend hours of theorycrafting and still not have scratched the surface. I'll exemplify these aspects of the game with a couple community/official youtube videos and assorted media. :D

Ability Mechanics: in PoE you equip skills by slotting gems into your gear, gems have only 2 requirements for use: a stat minimum (agi, int, or str) and character level. Not only are there skill gems the other key part of this system is the support gems, gems that modify the ability gem its linked with. This can be as simple as adding extra projectiles to your fireball spell (lesser multiple projectiles) to having a 6link combo of ability/support gems.

Here is a quick little explanation of the system: http://www.pathofexile.com/skills (a list of ALL gems is also located just at the start of the article in the link). And here is a neat little video on the system :D

As mentioned earlier there are also aesthetic mtx's that can be purchased which vary from alternate ability art, no-combat pets, and alternate armor art. (As of now the base visual characteristics of your toon is standardized for all players)

The Economy:

PoE operates on a completely barter based economy, gold/silver/dubloons/minerals/US$ do not exist. Instead there are roughly 20+ "currency" items. All of these items have their own use alongside their barter value, for example an alchemy orb turns a white (common) piece of armor/weapon into a yellow (rare) piece of armor/weapon of the same base type. Due to the malleability of these "currencies" values a good salesman/woman can operate a sort of dynamic forum shop selling with the ebb and flow of the games player demands. Here are some of them: http://www.pathofexile.com/item-data/currency !!

Currencies drop in the world as well as being attainable via the town hub vendors, each currency has a special sale recipe, for example to receive an alchemy orb you can collect pieces of gear with chaos resist and sell them to a vendor each piece of gear would then vendor for alchemy shard(s) comparable to the chaos resist value. (for anything here that sounds super complicated, the forums are chock full of starter guides as well as the well maintained wiki)

Gear:

Like most games of its genre PoE utilizes rarity tiers: white (common), blue (uncommon), yellow (rare), and orange (unique). From common to rare the difference lies in the amount of possible suffixes/prefixes a piece of gear can have, each prefix/suffix adds stats to an item for example: of the assassin suffix adds additional accuracy rating to the piece of gear. Unique items operate on a completely different model, usually created to diversify or encourage interesting builds they have affixes that afford massive consequences. Such as the unique gloves:

Combined with the barter/currency system every loot drop becomes substantial, you can vendor them for currency, trade them with other players, re-roll stats on the item for a better suited stat list or if its awesomesauce already you can :OOOO EQUIP IT!

Here is a little video of some of the cool builds you can make when you combine all three variables: support gems, ability gems and gear: (The developers are from New Zealand hence the accent)

End Game:

PoE's endgame consists of "Maps", maps start as white (common) drops with the only defining factor between differently titled maps being its base tile set used for randomly generating the map (as is the entire "regular" world of PoE), using currency you can beef up these maps to add additional mods, just like gear, such as "Monsters have x% increased attack speed" now of course it seems silly to be adding such a detrimental mod to a map BUT with each mod and its assigned "difficulty value" a % increased item drops value goes up, making maps a fun but dangerous way to test your character to the limits alongside hauling in teh phat lootz. As with any PoE content maps can be done in groups of up to 6 characters, each additional member of the party incrementally increases the base stats of the monsters you face as well as increasing the % increased drop rate value.

As far as PvP goes, with the coming launch of PoE Oct 23rd there will be both a 6v6 Capture the Flag and scheduled tournaments. Tournaments are a very exciting prospect, they run in a fairly novel fashion. A set time limit is allocated to the tournament event in which players compete to rack up the largest amount of points in multiple 1v1 arena fights.

PoE also runs all sorts of other scheduled PvE events such as race seasons, 4 month challenge leagues. Each race event has special modifiers on them that increase the difficulty compared to the "regular" standard or hardcore leagues, whether it be a time limit (A 1hour solo race for example) or a BLAMT race (Blood Magic, Ancestral, Lethal, Turbo). Here is a quick video explaining what was Season 1 of PoE's open beta race season (all the footage is taken from the open beta trailer and not at all representative of races >.<)

I think I've gushed too much already but if you have any further questions I would love to answer them!

(Apologies for any trainwreck sentences, wrote this up quickly after seeing this new? forum posted on facebook by Day[9]. Squeezed this quick write up in before bed :P )